1. Field of the Invention
The present invention relates to calcium sulfate based biomaterials, and methods for making such materials. These materials can be used as bone substitutes. In particular, the strength of the calcium sulfate added with sintering additives after firing is satisfactory. In addition, these materials show good biocompatibility.
2. Related Art
The volume and weight of the bones occupy the most parts of human's body. The main function of bones is to assist our bodies to take action and to support the body structure. As the flaw or damage is formed in bones, the clinical treatment is often required. The reasons causing such serious damages on bones are bone fractures, or bone tumor, or osteomyelitis, or collapses of vertebra, or the flawed hip bone, or the failed artificial joint. In order to resolve these damages, to replace the damaged bone with bone graft is still a common treatment in the clinics.
Nowadays, the bone graft comes from autograft and allograft. Autograft means the transplantation of organs, tissues or even proteins from one part of the body to another part in the same individual. This is a rather safe treatment. It may induce a good recovery. However, the source of autograft is limited. In addition, the elders, children or people who are not healthy are not suitable for such autograft treatment. Allograft means the transplantation of cells, tissues, or organs, sourced from the same species of a genetically non-identical human body. The bone graft in allograft may come from the bone bank. However, the quality of bones is questionable. For example, the disease, such as AIDS or hepatitis etc., may come with the surgery. In order to avoid the limitation and risk of autograft and allograft, using the artificial bone substitutes is becoming a popular alternative. Many medical companies in the world have therefore put their attention on developing bone substitutes.
The first bone graft was generated from Netherlands, by JobVan Meekren in 1668. In the 19th century, many doctors cured the fractures and damages of bones by using autograft. The results of surgeries were very successful. Till now, the technology of autograft is not changed too much, compared with that developed 100 hundred years ago.
Polymeric bone cement has been used as filler in orthopedics for quite a while. Since 1960, polymethylmethacrylate acid has been used to fill into the cavity between the artificial joint and bone tissue. It can fix the artificial joint in the bone tissue. Such bone cement has good fixing effect in the early stage; however, after implanting for a long time, the implanted component becomes loose because of stress shielding and foreign body reaction. In addition, one more operation is often needed to perform on 70% of the patient after implanting for 10 years. This circumstance results in wasting of money and inconvenience for doctors and patients. Although the bone cement can avoid the soft tissue to grow into defects and holes of bones, it still cannot be absorbed by human's body. The bone cement also can not be transferred into bone tissue. Furthermore, the high temperature and residual monomer generated during mixing bone cement will cause the death and toxic pollution of surrounding tissue. Therefore, many medical teams intend to use the absorbable bone substitutes, such as natural coral, hydroxyapatite, calcium phosphate, hemihydrate calcium sulfate or its mixture, to replace the traditional bone cement.
Calcium sulfate is massively used as the shaping molds in ceramic industry. The porous calcium sulfate can absorb water, but its strength is low. Therefore, the service lifespan of calcium sulfate used as molds is limited. If the strength of calcium sulfate can be improved, the service time will be extended. In addition, the calcium sulfate can be used as bulks and films in orthopedics because it has good biocompatibility and bio-degradability. However, the application of calcium sulfate is limited because it cannot be sintered and its strength is thus low.
Nowadays, the calcium sulfate products are made at room temperature (without sintering/heat treatment). This is the reason why the strength of calcium sulfate is poor after heat treatment. This is also the reason why the amount of calcium sulfate products is used less than that of calcium phosphate products used in the medical area.